The Alpha-Blaze HPX Lighted Nock contains a one-piece Nock/LED unit that is indexed with the vanes and press fits into the arrow s Aluminum Bushing. Upon firing the crossbow, the bowstring s force compresses the two pieces and activates the lighted nock. Deactivate the easy on/off Alpha-Blaze HPX lighted nock by pulling the nock straight out until the light turns off. The LED light of the Alpha-Blaze HPX system lasts for approximately twenty-four hours when activated Product Features Easy-to-Use one-piece HPX Nock / LED unit no assembly required Unmatched Durability Essential for Crossbow Hunting Required for Use with TenPoint Rail-less Crossbows TRX 515 AND TX 440. 515+ FPS approved Features a Nock Retention Groove that allows the user to both hear and feel the positive engagement of the nock to the string on TenPoint rail-less crossbows Bowstring activated Super bright LED light provides superior arrow flight visibility Easy deactivation 24-hour battery life when activated (approximate) Features TenPoint s Alpha-Nock HPX (all TenPoint & Wicked Ridge crossbows require the use of an Alpha-Nock arrow) Fits all TenPoint & Wicked Ridge arrows with a HP Aluminum Bushing (sold separately) 3 Lighted Nocks per pack Nock Weight: 27-grains